How to validate multiple Angular 2+/Ionic2+ form controls using one asynchronous function on submit?

My form have a FormGroup with many FormControls.

When clicking on submit a request is send to the backend with the data from the form.

In case of error, the server return an object containing error information for each field with error. I’ts not an per field validation. It’s a single validation that validates all fields.

How to set this errors comming from one single request in the respective FormControls?

See here.